1. Field of the Invention
The present invention relates to a light source control method and apparatus of an image scanner, and more particularly to a light source control method and apparatus of an image scanner which can automatically perform partial or full illumination and adjust brightness according to the scan area and the scan mode.
2. Description of the Related Art
Optical scanners are used to capture and digitize images. For example, an optical scanner can be used to capture the image of printed matter on a sheet of paper. The digitized image can then be electronically stored and/or processed with character recognition software to produce ASCII text. The typical optical scanner includes a light source, a linear array of photoelectric sensing elements (generally a CCD sensor or a CMOS sensor, or a CIS sensor), an analog amplifier, an analog to digital converter (ADC), a controller and a random access memory (RAM).
The CCD sensor includes a large number (e.g., 2000) of photoelectric sensing elements arranged in a linear array. Each photoelectric sensing element will capture light representing a single pixel of the image. The array will capture a line of pixels. By moving the CCD sensor across a document, the entire document can be scanned one line at a time.
The conversion into digital signals of light reflected from or transmitted through the document takes place in essentially three steps. First, each photoelectric sensing element will convert the light which it receives into an electric charge. The magnitude of the charge will depend on the intensity of the light and the exposure time. Second, the charges from each of the photoelectric sensing elements are converted into analog voltages via the analog amplifier. Finally, the analog voltages are digitized by the analog to digital converter for digital image processing and storage in the RAM.
In conventional image scanner, the light source always maintains constant illumination during scanning. However, constant illumination of the light source wastes power and is lack of efficiency when only part of scan area is needed to be scanned. Furthermore, constant illumination of the light source for multiple scan modes (Color, Gray and Line art) of an image scanner is not economical either. Hence it is desirable to provide a light source control method of an image scanner which can automatically perform partial or full illumination and adjust brightness according to the scan area and the scan mode so as to utilize the light source more efficiently and economically.